1. Field of the Invention
The present invention relates generally to control systems for air suspensions, and more particularly, but not by way of limitation, to a control system for overriding a vehicle's automatic air suspension leveling system such that the height of a vehicle's chassis relative to the vehicle's axle can be selectively altered.
2. Brief Description of the Related Art
Air suspension systems for vehicles, particularly trucks and buses, are well known. Such suspension systems generally include one or more air springs or air bags at each end of each axle such that a sprung mass which includes the chassis, body, and load of the vehicle is supported on an unsprung mass which includes the wheels, suspension, and axle.
Larger vehicles equipped with air suspensions, such as trucks consisting of a tractor and trailer are often also equipped with automatic leveling systems to maintain the height of the chassis of the tractor relative to the ground independent of the load supported by the trailer and/or the height of the chassis of the trailer relative to the ground. Many leveling systems comprise a regulating valve mounted on the chassis of the tractor and/or trailer and a leveling arm having one end operably connected to the regulating valve and another end linked to the axle of the tractor and/or trailer by a rigid rod. Thus, when the axle and chassis move relative to one another, such as when a load is placed on the chassis, the link forces the leveling arm to pivot. More particularly, when the leveling arm pivots upwardly because the chassis and axle have moved toward one another, the leveling arm opens the regulating valve so as to cause additional air to be introduced into the air springs, thus resulting in the chassis being raised relative to the axle. In contrast, when the leveling arm pivots downwardly because the chassis and axle have moved away from one another, the leveling arm causes the regulating valve to release or bleed air from the air springs, thus causing the chassis to be lowered relative to the axle.
While the automatic leveling system functions to maintain the chassis at a predetermined level relative to the axle, it is desirable to be able to selectively alter the clearance height between the chassis and the axle, particularly during loading and unloading operations, whereby the chassis of a tractor may be easily raised or lowered to mate with a loaded trailer thereby eliminating the driver from having to manually crank the trailer up or down to match the height of the tractor.
To this end, the present invention is directed to an improved override control system for overriding a vehicle's automatic air suspension leveling system such that the height of a vehicle's chassis relative to the vehicle's axle can be selectively altered.